The Jedi that died by shots were highly outnumberd. I have never seen a Jedi get shot in the face in a one on one fight.

As for the defensive stance of Kenshins, if he goes into it his sword is easily lost to the lightsaber, or he leaves himself open to many of Vaders Force powers.

There is no real way for kenshin to predict any of Vaders moves. At all. And without that he looses much of his power.

Speed won't do much for him against the powers of Jedi perdiction in battle. He needs to see only one swing of the swords, and cut it with his light saber. Thats it.

No way for kenshin to defend against a simple Force Push either. Vader has been shown to be able to use virtually every force power there is. With the Force speed he could even start to keep up with Kenshin, as for virtually every non-jedi his movements are extremely difficult to follow up on. So he is likely to be close to Kenshin's speed, if not matching it.

So to sum it up.

Kenshin
1)Ability to predict is worthless.
2)His extreme speed likely doesn't beat out Vader enough to make a difference.
3)His Defensive stance leaves him far to vulnerable to anything Vader is capable of Doing.
4)He has no defense against Vadars Force attacks.
5)His sword cannot even be blocked, so only decisive hits mean anything.
6)Since Vader is mostly machine, only critical blows are going to be effective in the slightest against him, and given his ability to predict, he can Guard himself agaisnt one who can't see his movements rather easily.

Aside from being a bit faster, Kenshins got nothing. His better sword technique doesn't mean much against the Force power possessed by Vader.